Acid/pH Adjustments
By Bill Collings (Revised August 1, 2007)
Overview
Winemakers frequently encounter challenges with grape acid and pH balance. Adjustment may be necessary when “the pH is too high and the acid too low,” when both are elevated, or when pH is low with high acidity—situations common in cool climate regions.
Key Measurement Information
Total acidity references use grams per litre throughout this guide. The conversion from percentage format involves moving the decimal point one position rightward (0.7% becomes 7 g/l).
Optimal pH Targets
The document recommends adjusting “all white and rosé musts to a maximum of pH 3.3 and all reds to a maximum of pH 3.4” using tartaric acid to “achieve optimum flavour extraction and to minimize bacterial infection.”
Adjustment Methods
Tartaric Acid Addition: The guideline suggests “1 g/l to reduce the pH by 0.1,” though actual results vary based on grape buffering capacity and may require lab testing.
Testing Procedure: Prepare a 10% tartaric acid solution in distilled water. Add varying amounts (1–3ml) to juice samples to determine proper dosage before treating the full batch.
Alternative Reduction Techniques:
- Water addition (10–15%) dilutes acidity without major pH changes
- Cold stabilization precipitates tartrates after fermentation
- Acidex® (calcium carbonate double salt) reduces both malic and tartaric acids when juice is stirred slowly into the compound
- Potassium carbonate works immediately at cold temperatures for fine-tuning
- Malolactic fermentation converts malic acid into lactic acid and carbon dioxide
Acid Types and Responses
Different acids affect total acidity differently: “a one-gram addition of tartaric acid will increase the TA by one gram per litre, malic acid will increase the TA by about 1.12 and citric acid by about 1.17.”
Index of Acidity (IA)
The IA calculation (TA minus pH) provides guidelines: dry red wines should target “an IA range of about 2 to 3, dry white wines about 2.7 to 3.7.” Values below these ranges produce flabby wines; values above create excessive sharpness.
Cool Climate Considerations
These regions frequently produce grapes with low pH/high TA or high pH/high TA combinations due to elevated malic acid and potassium levels. Recommended approaches include tartaric acid adjustments, Acidex® treatment, and malolactic fermentation for appropriate varieties.